1. Field of Invention
The present invention relates to a method for forming a semiconductor device. More particularly, the present invention relates to a method for patterning a material layer.
2. Description of Related Art
In the manufacture of integrated circuit, photolithography process is used to transfer patterns from a photo mask having customized circuit patterns to thin films formed on a wafer. The image transfer process comprises steps of forming a photoresist layer on a material layer, illuminating the photoresist layer through a photomask having the customized circuit patterns, developing the photoresist layer and then etching the material layer by using the patterned photoresist layer as a mask. Hence, the image transfer process is accomplished. For a well-manufactured integrated circuit product, the image transfer process mentioned above is performed several times to transfer the circuit patterns to each non-process layers to form the electrically circuit device.
Conventionally, in order to increase the integration of the device elements without being limited by the resolution of the optical tool, a double patterning process is developed. In the double patterning process, a mask layer is formed on the material layer and is patterned twice with using different photomasks. On the other words, the formation of photoresist layer, the exposure-developing process and the etching process for patterning the mask layer are repeatedly in sequence to transfer two different patterns into the mask layer. Then, by using the patterned mask layer, the material layer is pattern so as to transfer the pattern on the patterned mask layer into the material layer. Thus, the pattern in the mask layer possesses smaller pitch than the patterns of the photomasks. However, in the conventional double patterning process, the etching process should be performed several times. Therefore, the process procedure is complex and the throughput is decreased.